The Book of Judas is not part of the Christian canon. It's a Gnostic text that incorporates the idea that Yahweh is a false god who made this messed up world, and Jesus brought knowledge of the true God.
Saint Paul has said, 'All is permitted, but not all things are beneficial'. I think that gives an outline on exactly what a sin is and how it is applied to the human condition and helps to explain the apparent inconsistencies with the Bible. While it doesn't point to a specific code of conduct, it is leaving a very broad sense of what it is to be righteous and what it is to be holy. To be righteous as to what I understand it, is to be forgiving, to show hospitality, and mercy. We can do the things that are 'permitted but not beneficial', while still being considered righteous because God requires mercy and not sacrifice and he requires that we don't overindulge in things such as admiring the sparkle in our wine glass because of where it can lead; Admiring the luster in a glass of wine is to be lustful and it has lead to the love of things rather than the love of man. The Bible also seems to exclaim the consequences for actions such as bitterness (Lot's Wife), ruthlessness (Amorites), and scheming (Enam) and not so much as a punishment from God, but as a warning from God as to its consequence; If someone asks us not to touch a furnace because it is hot, and someone touches it, then who's fault is it really? The ruthless will be shown ruthlessness. The bitter will receive salt. The merciful will be shown mercy; What we give out is what comes back at us is what the Bible seems to be saying. And the revealing of human nature and what happens when man lacks faith (Lot and his daughters).
Many of the 'lost books of the Bible' are not written very well. The book of Thomas is just an apparent list of quotes from Jesus and has no literary structure to it at all.
What is an 'unusual' suppression of 'human nature'? What is human nature? So would argue that it doesn't exist and that the only thing that does exist is human behavior. If it was human nature to hurt and kill, then I think it would be useful to suppress these tendencies. If people have a tendency to go with multiple parters and it is understood that a committed monogamous relationship is not only healthy for society, but for the individual, then I would see that as a good thing and not a 'suppression' at all. Actually, I would argue that promiscuity is a form of supression, but I am a monogamous guy so maybe my opinion is biased.
Actually I have found in it a technology for achieving transcendent awareness. Further, as far as Christ teaching, was not even offered to everyone, but only to those who desired it and could understand what was being put forth as in, for those with ears to hear, or the well have no need of a physician. The idea that the bible is a behavioral code book is an egocentric interpretation. The ego finds its superior nature by condemning the nature of other egos.